Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $64.68   10.431%   $71.4268   $71.43   $71.45   $71.40  
  Purchase #2 $90.33   6.274%   $95.9973   $96.00   $96.00   $96.00  
  Purchase #3 $239.94   5.711%   $253.643   $253.64   $253.65   $253.60  
  Purchase #4 $178.33   12.513%   $200.6444   $200.64   $200.65   $200.60  
  Purchase #5 $60.69   12.676%   $68.3831   $68.38   $68.40   $68.40  
  Purchase #6 $144.28   9.837%   $158.4728   $158.47   $158.45   $158.50  
  Purchase #7 $68.27   7.431%   $73.3431   $73.34   $73.35   $73.30  
  7 purchase totals = $846.52       $921.9105   $921.90   $921.95   $921.80